Hazard warning and control systems, such as fire detection systems, and extinguishing control systems with fire detection and/or extinguishing control panels or detection systems with respective control panels present high demands on the reliability and operational safety of the systems, in order for the owners or operators of at-risk industrial units, storage units or other objects to be protected, to be warned in good time before the occurrence of great damage through fire, chemicals, sabotage, intrusion or other hazard scenarios, and/or in order for appropriate countermeasures to be taken, or automatic protection devices or means of alarm to be activated. Of particular importance is the activation of actuators, for example solenoid valves to activate extinguishing systems or actuators such as audible and visual means of alarm, for example flashing beacons and buzzers or actuators in the form of servomotors.
These actuators are activated by control devices of a hazard warning and control system through supply lines and/or signal lines, usually two-wire or multiple-wire lines, wherein in case of an incident an activation voltage UA conforming to the specifications will be switched to the actuators. The incident can for example be a fire incident, i.e. a burn- or fire detection signal or an intrusion or sabotage signal or another hazard or alarm signal.
Such installations must function reliably and error-free over longer periods of time under various requirements and operating conditions. To this end the supply lines and/or signal lines are continuously monitored to detect functional faults like short-circuits and wire breakages. Such monitored supply lines and/or signal lines are called primary lines or control lines. Hereinafter the term ‘control lines’ will be used. The monitoring for missing or faulty actuators is also of significance for the reliable operation.
The monitoring of supply lines and/or signal lines for wire breakage and short circuit for example in fire detection systems takes place thus far usually through a low control current that is caused by a resistance REOL at the end of the line, in particular a fire detection line, that is to be monitored. This monitoring current through the resistance plus the current uptake of the fire detectors on the line make the quiescent current that is continuously monitored by the control panel. If this quiescent current drops below a certain value, the control panel recognizes this as wire breakage on the line and signals this fault. The problem here is that the resistance REOL is very high in relation to the line resistance, thus a slow developing wire breakage, i.e. the gradual increase of the line resistance by a few ohms, is very difficult to measure by this ratio. However this is a mandatory requirement of standards, for example the EN54 series.
During long term operation of hazard warning and control systems the detection of the so called slow developing wire breakage is of great significance. By slow developing wire breakage a slow, gradual increase of the line resistance of the supply and/or signal lines is understood. Possible causes of this slow, gradual increase of the line resistance are environmental effects, as for example humidity and corrosive gases that lead to the oxidation of the contact points of the wires and the terminal contacts. This slow developing process leads to changes of the quiescent current on the respective lines in the range of approximately 0.1 mA, equivalent to only a 0.1Ω to 10Ω change of the line resistance.
Methods and devices of the aforementioned type are known from the prior art. A method and a device for monitoring a signaling line of a fire alarm system for faults is known from EP 1 855 261 A1, where a line current is applied to the fire alarm control system in operation, having a final element formed by a TVS diode. The line current and/or line voltage is monitored. Faults of the signaling line are detected through a short increase and a short drop of the line current. The evaluation takes place by means of the voltage levels, not the current. The evaluation is performed by the fire detection control panel, where the increase and decrease of the line current also takes place. The fire detection control panel continuously supplies the participants with the required operating voltage or activation voltage.
The disadvantage of this is that the nonlinear and temperature dependent behavior of TVS diodes at the end of the line makes it difficult to determine the absolute value of the line resistance, especially when a resistance increase of only a few Ω is to be determined.
WO 2009/087169 discloses a monitoring device and a method for monitoring the operational state of supply and/or signal lines of a detection system, in particular a fire protection and/or hazard warning system.
The monitoring device comprises a measuring device for generating a measurement signal, an evaluation device and a controllable signal source that is designed to inject a test signal into the supply and/or signal lines. The measurement signal comprises the system response of the supply and/or signal lines to the test signal.
The disadvantage here is that this device and the method is only suitable for relative measurements of the line resistance, and the fault detection, for example the detection of a slow developing wire breakage, always requires a calibration of the system during commissioning, the determined value of the system response is stored and becomes the reference value for the subsequent monitoring measurements. Thus increased line-resistance values on account of faulty installation cannot be detected.
FR 2 932 917 A1 discloses a safety system with an alarm control panel, a bifilar line and a line end module, where the alarm control panel is connected to a first end of the line and the line end module (monitoring module) is connected to a second end of the line, and several peripheral units are parallel-connected between the wires of the line. The alarm control panel of FR 2 932 917 A1 comprises a control unit, current supply means and measuring means, the measuring means being controlled by the control unit so as to detect a possible insulation failure of the line during a first monitoring phase and to detect a possible flux failure of the line during a second monitoring phase.
FR 2 932 917 A1 discloses a device for the detection of faults on the line of the safety system that in monitoring mode supplies the line by means of the current supply means of the alarm control panel with electric energy of inverse polarity, that leaves the peripheral units inactive, and in the monitoring phases injects two distinct defined currents from the alarm control panel into the line. The line end module is capable of assuming two states of impedance that are set through a sensor for detecting a phase change signal and a delay circuit. Furthermore FR 2 932 917 A1 discloses that the line end unit is equipped with an energy storage that is solely designated to supply the active components of the line end unit.
The EP 2 093 737 A1 document discloses an active line terminating module for monitoring a line impedance of electric systems, in particular for the usage at the end of fire detection lines, wherein a constant current sink with light indicator, a voltage regulator and an intelligent electronic component are arranged between the lines that are to be monitored, in such a way that the intelligent electronic component is connected through a line with the constant current sink.
Disadvantages of the prior art are:                the missing or inaccurate absolute determination of the line resistance in the region from mΩ to a few Ω;        previous methods and devices are expensive;        the complexity of monitoring devices with integrated measuring and evaluation devices within the monitoring device that are arranged at the end of a supply and/or signal line, distant from the supplying control panel, with associated environmental factors, makes these monitoring devices susceptible to EMC effects or requires high circuitry expenditures in order to suppress these;        participants on the supply and/or signal line distort the measurement of the line resistance;        during the measurement of the line resistance, voltage fluctuations on the supply and/or signal lines can distort the determination of the line resistance;        missing or inaccurate methods and devices for the measurement of the wire breakage, from slow developing to full wire breakage.        